000
ACUS01 KWNS 091941
SWODY1
SPC AC 091940
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0140 PM CST Fri Dec 09 2016
Valid 092000Z - 101200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
The risk for severe storms appears negligible across the U.S. today
through tonight.
No changes are needed with this outlook issuance.
..Peters.. 12/09/2016
.PREV DISCUSSION... /ISSUED 0958 AM CST Fri Dec 09 2016/
...SYNOPSIS...
Although cold surface ridging will remain prominent across most
areas east of the Rockies through this period, mid/upper flow has
trended more zonal within a belt from the mid-latitude eastern
Pacific through the Mid Atlantic Coast and western Atlantic. One
significant, but increasingly deformed/sheared impulse within this
regime will begin developing inland across the Pacific Northwest
coast later today. Associated pockets of colder air aloft and
large-scale forcing for ascent, in conjunction with relatively moist
low-level onshore flow, are expected to contribute to convective
development occasionally capable of generating lightning, mainly
west of the Washington Cascades. Otherwise, thunderstorm
probabilities elsewhere across the U.S. appear negligible.
$$

000
ACUS02 KWNS 091725
SWODY2
SPC AC 091724
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1124 AM CST Fri Dec 09 2016
Valid 101200Z - 111200Z
...NO THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Aside from one or two lightning strikes possible near the coast of
Washington and northwest Oregon, thunderstorms are not expected
Saturday through Saturday night.
...SYNOPSIS...
Models maintain a low-amplitude/quasi-zonal flow aloft through this
forecast period. A stable boundary layer across much of the U.S.
will tend to hinder the development of deep moist convection.
...Coastal areas of WA and northwest OR...
Steepening lapse rates across coastal areas of WA/northwest OR
Saturday afternoon, as a progressive midlevel shortwave trough and
attendant cold front reach this region, should support low-topped
convection. Most of these showers should form offshore within the
post-frontal air mass before moving ashore. Forecast soundings
suggest instability will be quite low, though buoyancy may become
deep enough for lightning production. Overall coverage is expected
to remain less than 10 percent, precluding the inclusion of a
general thunderstorm outlook area.
..Peters.. 12/09/2016
$$

000
ACUS03 KWNS 091630
SWODY3
SPC AC 091630
Day 3 Convective Outlook RESENT 1
NWS Storm Prediction Center Norman OK
1030 AM CST Fri Dec 09 2016
Valid 111200Z - 121200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Thunderstorms may occur across parts of the lower and mid
Mississippi and Ohio Valleys Sunday. Showers and a few/occasional
lightning strikes may also occur over portions of the coastal
Pacific Northwest.
...SYNOPSIS...
While solutions continue to differ -- both between the various
models and also from run to run within the same model, some
amplification of the upper flow field across the U.S. appears likely
to occur Sunday, as short-wave troughing embedded in the
fast/cyclonic westerlies moves quickly out of the Rockies and across
the north-central portion of the country. As this occurs,
cyclogenesis is forecast as a lee low -- initially over the central
high Plains vicinity -- moves northeastward toward the Ohio
Valley/upper Great Lakes while deepening. A trailing cold front is
forecast to shift southeastward across the southern Plains and
mid-Mississippi Valley overnight.
...mid and lower Mississippi/Ohio Valleys...
While warm-sector thunderstorms appear unlikely at this time across
the Sabine River Valley area of east Texas and western Louisiana
during the day, isentropic ascent/warm advection atop a cool
continental boundary layer will occur ahead of the developing
surface low and associated frontal system on Sunday. Moistening
aloft is expected to result in eventual elevated destabilization
sufficient for development of showers and scattered thunderstorms --
from roughly the mid Mississippi to the mid Ohio Valleys. While
uncertainty remains regarding pattern evolution, and thus details of
convective potential, thunder risk apparent at this time warrants
inclusion of a 10% area, but with destabilization likely
insufficient to support appreciable hail potential.
...coastal Pacific Northwest...
Fast west-northwesterly upslope flow in the lower and middle
troposphere combined with a pocket of cold mid-level air (-34 C at
500 mb) spreading across the area will support showers -- and
occasional lightning -- across coastal mountain ranges of WA and OR
Sunday. Lack of sufficient CAPE for robust updrafts will preclude
any appreciable severe risk.
...southeast U.S. coastal areas...
Scattered showers, and possibly a couple of thunderstorms, may occur
across FL through the day, and could spread northward into the
coastal Carolinas overnight.
..Goss.. 12/09/2016
$$

ACUS48 KWNS 091639
SWOD48
SPC AC 091637
Day 4-8 Convective Outlook RESENT 2
NWS Storm Prediction Center Norman OK
1037 AM CST Fri Dec 09 2016
Valid 121200Z - 171200Z
...DISCUSSION...
The latest GFS and ECMWF runs exhibit a fairly good degree of
model-to-model similarity, with both shifting a large vortex
southeastward across the Canadian Prairie and then eastward across
Quebec and Ontario days 4-6 (Monday through Wednesday). However,
differences in the amplitude of the surrounding cyclonic flow field
extending into the central and -- eventually -- the eastern U.S. are
noted, with the ECMWF noting more pronounced/amplified cyclonic flow
across the U.S. than the more zonal GFS. As a result, the ECMWF's
surface baroclinic zone advances much more quickly southward across
the south central and southeastern U.S. than the GFS's front. By
the afternoon of Day 6/Wednesday, the GFS depicts the front from
southeast VA west-southwest across the southern Appalachians and
central Gulf coast states, while the ECMWF places the front across
northern FL and the northern Gulf of Mexico. While fast flow aloft
would provide ample shear for stronger storms should sufficient CAPE
evolve ahead of the front, the aforementioned model differences
preclude any reasonable attempt to highlight any severe weather risk
areas at this time.
By Day 7 and particularly Day 8, larger-scale differences begin to
emerge between the models, yielding steadily increasing uncertainty
through the end of the period.
..Goss.. 12/09/2016